Genomic insights into methicillin-resistant Staphylococcus aureus from Swiss wastewater and clinical samples

The study analyzed whole-genome sequences of 115 methicillin-resistant Staphylococcus aureus (MRSA) isolates from Switzerland collected between 2021 and 2024, including 89 from hospitals and 26 from wastewater treatment plants. Clinical isolates showed greater genetic diversity with 23 sequence types and 46 spa types, while wastewater isolates contained only 6 sequence types and 9 spa types. All wastewater isolates (100 percent) and most clinical isolates (64 percent) carried SCCmec IV type, historically associated with community-associated MRSA. Panton-Valentine Leukocidin genes were detected in 37 percent of all isolates. One wastewater sequence type (ST97) was genetically distinct and corresponds to a known livestock-associated MRSA lineage. The findings suggest that wastewater analysis supplements traditional MRSA surveillance methods but provides limited unique insights into clinical circulation.